IMS is a subsystem proposed by the 3rd Generation Partnership Project (3GPP) which supports IP multimedia services. The essential feature of the IMS is the realization of the separation between service management, session control and bearer access with the deployment of the Session Initiation Protocol (SIP) as the call control protocol. The IMS is a multimedia control/call control platform over a packet domain and supports both session and non-session multimedia services. The IMS provides a general service platform for multimedia applications.
FIG. 1 illustrates a partial architecture diagram of the IMS, in which a Call Session Control Function (CSCF) is a central control part in the IMS core network and is responsible for subscription authentication of a User Equipment (UE) and session control. The CSCF performs basic session route function with respect to the calling and called users and conducts route trigger for valued added services to an Application Server (AS) and service control interaction when a condition is met, according to IMS Initial Filter Criteria (iFC) subscribed by the user. A Home Subscriber Server is a user database server which saves IMS subscription information of the user, i.e., association information between the user identity and user subscription data. When the user conducts a service operation, related entities in the IMS, such as an Interrogating CSCF (I-CSCF), a Serving CSCF (S-CSCF) and the AS, obtain the subscription data of the related user from the HSS, through the user identity. In the IMS subscription information, a set of user subscription data related to the service is referred to as a Service Profile (SP).
FIG. 2 is a diagram illustrating the relationship between the user identity and the SP. As shown in FIG. 2, the user identity includes an IMS Private User Identity (IMPI) and an IMS Public User Identity (IMPU). An IMPI belongs to only one IMS subscription and one IMS subscription may include a plurality of IMPIs. An IMPI may include a plurality of IMPUs and an IMPU may be shared by a plurality of IMPIs. An IMPU has only one SP and one SP may be shared by a plurality of IMPUs.